HNOI2002

 对于当天的营业额，你要找到之前的数和他差的绝对值最小的和。由于这个是不断在插入的，所以用伸展树来维护。

http://www.lydsy.com/JudgeOnline/problem.php?id=1588

照着kuangbin大牛的代码敲下来的。

#include<map>
#include<set>
#include<queue>
#include<stack>
#include<cmath>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#define INF 99999999
#define ll __int64
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
using namespace std;
const int MAXN = 100005;
int pre[MAXN],key[MAXN],ch[MAXN][2],root,tot;
//父亲结点 键值 左右子树 根节点 节点数量
int n;
void Newnode(int &rt,int pa,int k)
{
    rt = ++tot;
    pre[rt] = pa;
    key[rt] = k;
    ch[rt][0] = ch[rt][1] = 0;//空
}

void Rotate(int x,int kind)
{
    int y = pre[x];
    ch[y][!kind] = ch[x][kind];
    pre[ch[x][kind]] = y;
    if(pre[y]){
        ch[pre[y]][ch[pre[y]][1]==y] = x;
    }
    pre[x] = pre[y];
    ch[x][kind] = y;
    pre[y] = x;
}

//将结点rt 调整到goal下面
void splay(int rt,int goal)
{
    while(pre[rt] != goal)
    {
        if(pre[pre[rt]] == goal)
            Rotate(rt,ch[pre[rt]][0]==rt);
        else {
            int y = pre[rt];
            int kind = (ch[pre[y]][0]==y);
            if(ch[y][kind] == rt){//rt 和 pre[rt]不在同一方向上
                Rotate(rt,!kind); //kind=1时，说明rt在y的右边 而y在pre[y]的左边
                Rotate(rt,kind);
            }
            else {
                Rotate(y,kind);
                Rotate(rt,kind);
            }
        }
    }
    if(goal == 0)
        root = rt;
}

int Insert(int k)
{
    int rt = root;
    while(ch[rt][key[rt]<k]){//如果key[r]<k，表明当前k在右边，不然去左边
        if(key[rt] == k){
            splay(rt,0);
            return 0;
        }
        rt = ch[rt][key[rt]<k];
    }
    Newnode(ch[rt][key[rt]<k],rt,k);
    splay(ch[rt][key[rt]<k],0);
    return 1;
}

int get_pre(int rt)
{
    int tmp = ch[rt][0];
    if(tmp == 0)
        return INF;
    while(ch[tmp][1])
    {
        tmp = ch[tmp][1];
    }
    return key[rt] - key[tmp];
}

int get_next(int rt)
{
    int tmp = ch[rt][1];
    if(tmp == 0)
        return INF;
    while(ch[tmp][0])
    {
        tmp = ch[tmp][0];
    }
    return key[tmp] - key[rt];
}
int main()
{
    int i,j;
    while(~scanf("%d",&n))
    {
        root = tot = 0;
        int ans = 0;
        for(i=1; i<=n; i++){
            int num;
            if(scanf("%d",&num)==EOF)num = 0;
            if(i == 1){
                ans += num;
                Newnode(root,0,num);
                continue;
            }
            if(Insert(num) == 0)
                continue;
            int a = get_pre(root);
            int b = get_next(root);
            //cout<<a<<" "<<b<<endl;
            ans += min(a,b);
        }
        printf("%d\n",ans);
    }
}